The Digital Reader links to Mental Floss on the vexing question of why do some books contain blank pages? I guess just saying “even working” isn’t really enough for everyone interested in books; maybe also for everyone working in publishing. So here goes.
Books are made of paper. They are not printed one page at a time like your computer’s printer, though of course in theory they could be.* It would just be too expensive to do that. They are printed more than one page at a time in order to make them cheaper. If you take a bit of paper and fold it in half, you will find you have four bits that look like pages. Fold it again, and you’ve got eight; again and it’s sixteen, and so on. The science of getting your pages in the right sequence is called Imposition.
If your book is three pages long, there is no way, other than writing more copy, that you can avoid it having a blank — even if you did insist on printing it one page at a time. By the same mathematical logic, if your book is 126 pages long, there’s no way you can avoid two blanks, because if you did tear two pages out the corresponding two pages at the other side of the gutter fold would also fall away.
Most books nowadays are printed on web presses, and there the “ideal” number of pages will depend on the individual press, but there’s no way that you can avoid multiples of at least four. When we used to print books sheet-fed (i.e. on sheets of paper rather than a continuous roll, a web of paper) 128 was the most efficient way to go. In other words presses were built to print 64 pages of a 6⅛” x 9¼” standard book. As they would have to print both sides, 64 + 64 obviously made for 128. We would spend much time trying to force books into 128, 256, 384, 512 pages or the 64- and 32-page steps in between. One obvious easy way would be to add blanks to get to the next step. The assumption by readers that fewer pages will cost less to print is unfortunately not true (except in these 32 or 64 page-type steps). If your book totals 365 pages of front matter, text and back matter, you could make it 368 pages, but not 366, which isn’t divisible by 4 (so the other end of the missing two would also fall out). This would mean you were going to impose the book so that it would print as if it were a 384 page book, but with 16 blank pages which would go through the press without receiving any ink, and then would have to be cut away before the book went into the bindery. While this could be done, it would cost you more than leaving the 16 blanks there. You wouldn’t save anything, and cutting out 16 pages would actually cost you something. Much cheaper to take these blanks and distribute them before and after the book. I would take 4 blanks and put them in the front of the book and allow the other 15 to “print” at the end of the book, after the index. I might have made it 6 at the front and 13 at the back. The point is though that it is cheaper to include these blanks than to pay to avoid them. Of course, if you were making a de luxe book, you wouldn’t hesitate to spend the money to get rid of that extra 16 pages, leaving only 3 blanks at the back, but in most cases you wouldn’t want to “waste” the money. After all what harm does it do the reader to have blanks at the back of the volume?
Certain blanks are built in to the structure of the book. It is a rule of book making that after the very first page of print there shall be no blank rectos. So your first page will be the half title page, a recto, and this will be followed by a blank, then the title page, which will have copyright information on the back. And so on. If the last page of the Preface ends on a recto, and will be followed by page 1 chapter 1 of the book, a blank verso will be inserted so that page 1 appears on a recto. These are just rules of polite book-making, but if you use books at all, flicking back and forth between index, endnotes, text, you will be driven quickly mad if the odd number pages are not always on the right hand side of the page spread.
* and in the case of print-on-demand digital printers, now are.